1. 1 Human Error ● Definition – an occasion “… in which a planned sequence of mental or physical activities fails to achieve its intended outcome, and when these failures cannot be attributed to the intervention of some chance agency.” – James Reason ● Broad Classes of Human Errors – Planning Failures: Mistakes inappropriate plan, misdirected intention plan carried out as intended e.g., wrong medication prescribed & administered – Execution Failures Slips –appropriate plan, intention –part of plan performed incorrectly –e.g., trocar injury Lapses –appropriate plan, intention –part of plan omitted –e.g., forget to remove sponge before closing

2. 2 Rasmussen / Reason Model of Human Performance goal / problem recognized goal achieved initiate “automatic” process with attentional checks Skill-BasedRule-BasedKnowledge-Based consider state info apply If-Then rule problem resolved ? familiar pattern ? try to find analogy revert to mental model, analyze deduce, infer, plan, execute problem resolved ? found ? yes no yes no yes no yes no

3. 3 Reason’s Error Taxonomy (partial) ● Skill-Based Errors – double-capture slips (distractor capture + strongest schema capture) – omissions (lapses) following interruption – reduced intentionality (prospective memory errors) ● Rule-Based Errors – first exceptions (strong-but-now-wrong rule) – information overload – wrong rule ● Knowledge-Based Errors – selectivity (salience > importance) – working memory limitations – anchoring / confirmation bias – illusory correlation – problems with complexity ● delayed feedback ● serial vs. network causality ● thematic vagabonding (flitting from issue to issue)

4. 4 Understanding Human Error: The AORTA (Stage) Model of Human Performance Attend Observe Remember ThinkAct attend to one task attend to several tasks see/read hear feel (palpate) detect discriminate recognize perceive memorize recall (long-/short-term) maintain mental model calculate decide solve develop alternatives choose alternative select response reach grasp move/manipulate speak walk/run respond Environment stimuli responses

5. 5 Human Performance Database V 2.5

6. 6 6 Human Error and Accidents Causes of Adverse Events Rarely individual incompetence lack of due diligence bad luck Commonly Vulnerable Systems* Fallible Humans* * from E.L. Wiener, “Fallible Humans and Vulnerable Systems: Lessons Learned from Aviation,” 1987

7. 7 Some Common Human Fallibilities Attend Observe Remember ThinkAct limited attentional resources attraction to salient but irrelevant cues inability to focus attention: distraction inability to divide attention: tunneling Environment stimuli responses

8. 8 Some Common Human Fallibilities Attend Observe Remember ThinkAct detection thresholds limited visual field sensory impairments auditory masking discrimination thresholds vigilance loss Environment stimuli responses

9. 9 Some Common Human Fallibilities Attend Observe Remember ThinkAct limited working memory capacity (7 + 2 “chunks”) limited working memory duration (< 20 sec) inefficient chunking verbal/spatial dominance weak long-term memory associations Environment stimuli responses

10. 10 Some Common Human Fallibilities Attend Observe Remember ThinkAct anchoring, confirmation bias recency bias tendency to treat all sources as equally reliable bias against absence of cues asymmetric valuation (gain/loss) overconfidence erroneous mental model Environment stimuli responses

11. 11 Some Common Human Fallibilities Attend Observe Remember ThinkAct anthropometric limits neuromuscular limits strength limits response time considerations speed/accuracy tradeoff Environment stimuli

12. 12 Failure Modes and Effects Analysis ● A#, Activity / Process / Function ● Contributing Factors ● Potential Failure Mode ● Potential Effects of Failure Mode ● Severity ● Probability ● Nondetectability ● RPN: Risk Priority Number ● Potential Remediations ● Design Requirements

13. Fault Tree Analysis (FTA) ● Purpose – (To determine the events and conditions leading up to an adverse event.) – (To determine the probability of an adverse event.) ● Approach – Identify potential adverse event. – Identify AND/OR combinations of events that lead to the adverse event. – Continue analysis as far as possible/reasonable. – (Determine individual event probabilities and compute probability of adverse event.) ● Symbols

14. Fault Tree Aanalysis Example (based on Konz & Johnson, Work Design, 7 th Ed., Fig. 20.2, p. 383)

15. FTA Example p = 0.1p = 0.01

16. FTA Example p = 0.1p = 0.01 p = 0.12 p = 0.01 Simplifying Assumption: P(A or B) = P(A) + P(B) (i.e., A and B independent)

17. FTA Example p = 0.1p = 0.01 p = 0.12 p = 0.01 p = 0.13 p = 0.1

18. FTA Example p = 0.1p = 0.01 p = 0.12 p = 0.01 p = 0.13 p = 0.1 p = 0.23 p = 0.01

19. FTA Example p = 0.1p = 0.01 p = 0.12 p = 0.01 p = 0.13 p = 0.1 p = 0.23 p = 0.01 p = 0.0023

20. Hazard Propagation Model of Occupational Safety “Causes:” Unsafe ConditionsUnsafe Acts Contributing Factors: Electrical Hazards Mechanical Hazards Pressure & Toxic Substance Hazards Physical Hazards Equipment Interfaces Personnel Characteristics Social Factors Human Error Job Characteristics Control: Control At the Source Control On the Path Control At the Receiver Receiver Path Hazard (Source)

21. Control At the Source Example: Machine Guarding ● OSHA Machine Guarding Regulations: – http://www.osha.gov/SLTC/machineguarding/index.html http://www.osha.gov/SLTC/machineguarding/index.html ● Machine Guarding Checklist